1. Field of the Invention:
The present invention relates to the preparation and use of molecules carrying attached thereon metal complexing agents or biotin-containing detectable groups, as well as the products themselves.
2. Description of the Prior Art:
The use of radioactively labelled diagnostic and therapeutic agents obtained by labeling such agents with metal ions has recently received renewed interest. In this technique, a chelating moiety is covalently attached to the molecule of interest, and a radioactive ion is chelated by the sequestering groups of the chelator. The radioactively labelled agents can then be used both in vitro (for example in radioimmunoassay systems) and in vivo (for example, both in diagnostic imaging techniques and in radiation therapy techniques). The use of metal labelling of the nonradioactive type is also of interest, as for example, in the utilization of nuclear magnetic resonance, electron spin resonance, catalytic techniques, and the like.
Different metal chelating groups have been attached to biopolymers in the prior art. Activated analogues of ethylenediaminetetraacetic acid (EDTA) derived from 1-(p-benzenediazonium)EDTA (I) have been used on proteins: ##STR4##
(See, for example, Meares et al. U.S. Pat. No. 4,043,998, Sundberg et al. Journal of Medicinal Chemistry 17: 1304-1307 (1974); or Sundberg et al., Nature 250: 587-588 (1974).) The p-benzenediazonium EDTA of formula I is coupled via an azo linkage to selected tyrosine, histidine or amine residues of proteins, the latter forming triazines which are acid labile.
Diethylenetriaminepentaacetic acid (DTPA) is a metal chelator which has also been attached to polypeptides (see, for example, Krejcarek et al Biochemical Biophysical Research Communications 77: 582-585 (1977), Hnatovich Science 220: 613-615 (1983), or Khaw, ibid, 209: 295-297 (1980).) The chelator is attached through one of its carboxyl groups via an amide linkage to a protein-derived amino group, as shown in formula II: ##STR5##
This DTPA conjugate is achieved by first preparing the di-anhydride and reacting the same with a protein. (See for example, Scheinberg, Science 215: 1511-1513 (1982).) Involvement of the di-anhydride, however, may cause potential crosslinking problems which are either intramolecular or intermolecular. Also, attachment of the chelator through one of its carboxy groups may remove this carboxy group from consideration as a complexing moiety, thus decreasing the chelating efficiency, by a modification of the binding affinity constant and geometry.
Wieder et al U.S. Pat. No. 4,352,751 also suggest the attachement of metal chelating groups to proteins, utilizing trans-diaminocyclohexanetetraacetic acid (DCTA), attached through one of its carboxy groups to the amino group of a protein. As a model, Wieder et al show the reaction with ethylamine to form compound (III): ##STR6##
This compound may suffer from the same problems as the DTPA complex, in that conjugation occurs through one of the carboxy groups, thus potentially decreasing the binding affinity, and modifying the geometry of the resulting metal complexes.
Other metal chelating groups have also been attached to biopolymers, e.g., methylpicolinimidate on lysozyme (Benisek et al, J. Biol. Chem., 243: 4267-4271 (1968)), ferritin on monoclonal antibodies (Block et al, Nature 301: 342-344 (1983)), and the like.
A possible means of overcoming the aforementioned problems of loss of affinity, limitation on protein reactive residues, and change in geometry or crosslinking is disclosed in commonly assigned copending patent application Ser. No. 391,440 filed on June 23, 1982 for "Modified Nucleotides, Methods of Preparing and Utilizing, and Compositions Containing the Same" by Engelhardt et al, which is herein fully incorporated by reference. The Engelhardt et al application discloses the coupling of a thiocyanate derivative of DCTA to an allylamine-modified deoxyUTP and its possible incorporation into polynucleotides. See IV: ##STR7##
The use of the deoxyUTP allylamine and its attachment to other detectable groups, such as biotin, has also been disclosed (See, for example Langer et al Proc. Nat. Acad. Sci. 78: 6633-06637 (1981) or copending U.S. application Ser. No. 255,223 filed Apr. 17, 1981 at the U.S. Patent and Trademark Office to Ward et al, entitled "Modified Nucleotides and Methods of Preparing and Using Same," herein incorporated by reference).
There would be an advantage to utilize the DCTA chelating agent or other chelating agents without having to extensively modify nucleotides a priori, to utilize physiological chemical process conditions, and to provide a wide range of alternative methods utilizable in polypeptide, polynucleotide, polysaccharide and small molecule chemistry.
The development of such methodology would allow the use of high affinity, versatile metal chelating agents such as DCTA, and might also be extended and applied to the attachment of other chelators or detectable moieties, such as biotin.